Ceramic magnetic material with a small temperature coefficient



pounds are not those Patented Aug. 21, 1951 CERAMIC MAGNETIC MATERIAL WITH A SMALL TEMPERATURE. COEFFICIENT Ernst Albers-Schoenberg, Metuchen, N. J., as-

signor to Steatite Research Corporation, 1Keasbey, N. J., a corporation of Delaware No Drawing. Application May 26, 1949,

1 Serial No. 95,582

6 Claims. (01. 252 -625) This invention relates to a ceramic magnetic material, especially for transformer and inductance coils, with ;a small temperature coefficient and to the process of making the material.

Recently a number of ferrite compounds have been developed and described in the technical literature, i. e. ferromagnetic oxides of the general formula MFe2O4, where M represents a bivalent metal as, for instance, manganese, copper of magnesium. Each of these ferrites which form crystals of the same shape as the magnetite, F8304, has a different magnetic permeability ohmic resistance, Curie point and magnetic losses. On the whole, these compounds or suitable mixtures of them cover a rangeo'f initial permeability (,uo) from very low figures below 30 up to high values of more than 1000, the ohmic resistance varying between 10 to 10 ohms cm. As a rough rule it has been found that the highest initial permeability is associated with a fairly low Curie point, while Curie temperatures above 200 C. are found to be related to a medium or a low initial permeability and the conductivity, which always shows an increasing tendency with an increase f 11..

There exists an analogy in some extent between the dielectrics based on titania and titania compounds and the ferromagnetic ceramic bodies, as the dielectric constant K can be compared to the permeability and the dielectric losses to the magnetic losses. But in the field of dielectrics it I has been proved,- that the most valuable comwith the highest possible K because the variation of K with temperature of these bodies is so large that condensers, made of such bodies have an intolerable deficiency in temperature constancy. The most valuable dielectrics, therefore, especially for high frequencydevices, have been found on a lower K-level, where, besides a low-power factor, temperatures coefficients of K close to zerocan be obtained.

1 An object of the invention is to provide a ferromagnetic compound having better than average magnetic properties such as permeability, initial permeability, Curie point and magnetic losses and at'the same time having a very small temperature coefficient of n. 1

Another object of the invention is to provide a ferromagnetic compound having better than average magnetic properties such as permeability,

initial permeability, Curie point and magnetic losses and at the same time having a temperature coefficient which is no higher than that of an air coil.

Another object of the invention is to provide a shaped ferromagnetic body having a Curie point of 250 C. or higher, small magnetic losses and at the same time having a very small temperature coefficient and said body consisting of a crystalline cubic phase and a glassy intercrystalline phase.

Another object of the invention is to provide a process of making such products.

These objects and others ancillary thereto are obtained by combining four bivalent oxides, MgO, MnO, ZnO and NiO and F8203 and a small amount of $5.02. The mol ratio between the total amount of bivalent oxides and the F8203 must be approximately 1:1. The mol ratio between the bivalent oxides and the S102 lies within the limits of 05-35 MgO .10-.25 MnO .15-.30 ZnO: .5-.40 NiO .10-.20 SiOz. Extremely small temperature coefilcients are attained, if the mol ratio lies within the range of .20-.30 MgO .l0-.15 MnO .20-.30 ZnO .15- -.20 NiO .15.20 S102.

Such ferrite compounds have an initial permeability of between about and 150, small magnetic losses over the frequency range of cs. to about 30 mos, a Curie point of 250 C. or higher, a temperature coefficient measured on toroidal cores of not more than 10% for C. temperature increase. This figure of 10% corresponds to a much smaller figure of 1 to 2% only, if the material is used as a cylindrical core in an inductance coil.

Coils equipped with cores of such materials show no higher temperature coeii'icient than an air coil.

If these bodies would be prepared of only the pure bivalent oxides and the trivalent F8203 the fired product would consist of a polycrystalline aggregate presenting only one phase. Materials of this kind are somewhat unfavorable on two accounts. It is known that crystalline aggregates without any intermediate glassy phase sometimes have a tendency to disintegrate. This effect, for instance, is well known from the magnesium silicates which, if formed of merely MgSiOs crystals lacking a protective glassy phase, can disintegrate within a few days after firing into a fine powder. Even if the disintegration does not progress to completion a noticeable change of the physical properties may take place. In the second place, in the special case of magnetic iron oxides an intermediate glassy phase created by the addition of silica improves not only the insulating properties, diminishing some losses, but eifects also a considerable decrease of the temperature-coefficient of the magnetic permeability. It goes without saying that the silica has to be added in a very finely divided state to be sufiiciently reactive. To facilitate and to support the formation of the glassy phase one or more oxides of univalent elements such as lithium, sodium or potassium may be added in amounts up to about 0.05 mol.

The components which appear in the final product are not necessarily added to the composition in that form. For example, manganese is usually added in the form of the dioxide, but during the firing process it is changed to the monoxide. When lithium, sodium and potassium oxides are desired in the final product the carbonates of these metals are usually added to the original composition. The various components of the powder from which the products are molded are ground and mixed together by milling, etc. The powders are preferably ground ver fine, to less than 0.010 m. m., for example. The mixed powders are moistened with just enough aqueous liquid to make the unfired product adhere when molded. The aqueous liquid may be ordinary water or it may be water having wax or other binding material emulsified therein. The moistened powder may be molded in a steel die or other ceramic molding machine such as an extrusion machine. The molded product must be fired at a temperature high enough to cause a phase separation between the cubic crystalline ferrite materials and the glassy constituents.

The novel features characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying examples:

Example 1 A mix of the following ingredients in the proportions indicated is compounded:

Mol ratio: .20 MgO:.15 MnO:.25 ZnO:.20 NiOZ.15 $1021.05 LizOZLO F6203.

Composition 3.5 MgO 6.0 M1102 8.5 ZnO 6.5 NiO 1.5 LizCOz 4.0 SiOz 70.0 FezOs uct are the following:

Initial permeability (l-3 megacycles) 115 Curie point C 270 Temperature coeflicient of (toroid) 10% change between room temperature and 120 4 Example 2 A mix is made of the following ingredients in the proportions indicated:

M01 ratio: .08 Mg0:0.19 MnO:.19 ZnO:.36

NiO:.05 Li2O:.14 8102:.92 Fezoa.

Composition 1.5 MgO 7.5 M1102 7.0 ZnO 12.5 M0

1.5 LizCOs 4.0 SiOz 68.0 F8203 The preparation and molding is done in the same way as mentioned in Example 1.

The properties of the fired material are these: Initial permeability (1-3 mos.) Maximum permeability (D. C.) 300 Curie point C 275 Temperature coefiicient of (toroid) 5% change between room temperature and C.

Example 3 A mix is made up of the following ingredients in the proportions indicated:

Mol ratio: .25 MgO:.14 MnO:.25 ZnO:.16 NiO:.20 81022.92 F6203.

Composition 5.0 MgO 6.0 MnOz 10.0 ZnO 6.0 N10 73.0 FezOa 6.0 S102 The preparation and molding is done in the same way as mentioned in Example 1.

The physical properties of this material are shown in the following table:

Initial permeability (1-3 mos.) 90 Curie point C 265 Temperature coeflicient of (toroid) 1-3% change between room temperature and 120 C.

I claim:

1. A ferromagnetic ceramic material consisting mainly of iron oxide compounds of the magnetitetype, suitable for the use at frequencies between 60 es. and about 30 mos, composed of the four bivalent metal oxides, MgO, MnO, ZnO, and NiO, silica and F6203, in the mol ratio of .05-.35 MgO .10-.25 MnO .15-.30 ZnO .15-.40 N10 .10-.20 S102 about 1 F6203 the total mol proportion of the bivalent metal oxides to F8203 being approximately 1:1 said material having'a Curie point of at least 250 C. an initial permeability between 50 and and a temperature coefficient of a (measured on a toroid) of less than 10% between room temperature and 120 C.

2. A shaped ferromagnetic ceramic article consisting mainly of iron oxide compounds of the magnetite type, composed of MgO, MnO, ZnO, NiO, F8203 the total mol proportion of the bivalent metal oxides being approximately equal to the mol proportion of F9203 and an amount of about .2 mol of silica (per mol proportion of F8203) said material forming a heterogeneous body of a crystalline cubic phase and a glassy intercrystalline phase, the material of said article having a Curie point of at least 250 C'. an initial permeability of about 50 to 150 and a temperature coefiicient of a (measured on a toroid) of less than 10% between room. temperature and 3. A ferromagnetic ceramic material consisting essentially of iron oxide compounds of the magnetite type, composed of about 1 mol proportion of MgO, MnO, ZnO and N10, 1 mol total proportion of F6203 and an amount of about .1.2 mol of silica and about 0.05 mol of an univalent metal oxide, per mol proportion of F8203, said material consisting of a heterogeneous body of a crystalline cubic phase and a glassy intercrystalline phase and 9, having a Curie point of at least 250 0., an initial permeability of about 50 to 150 and a temperature coefiicient of ,1 (measured on a toroid) of less than between room temperature and 100 C.

4. A ferromagnetic ceramic material consisting essentially of iron oxide compounds of the magnetite-type, composed of the four bivalent oxides, MgO, MnO, ZnO, and NiO, silica and F8203, in the mol ratio of 20-30 MgO .10-.15 MnO 20-.30 ZnO .15-.20 NiO .15-.20 S102 about 1.0 F6203, the total mol proportion of the bivalent metal oxides to F6203 being approximately 1:1 said material having a Curie point of at least 250 C. an initial permeability of 70-100 and a temperature coefficient of u (measured on a toroid) of less than 3% between room temperature and 120 C.

5. A process of makin a shaped ferromagnetic body consisting essentially of iron oxide compounds of the magnetite type, which body consists of a heterogeneous body having a crystalline cubic phase and a glassy intercrystalline phase comprising the steps of mixing together F6203 and compounds of Mg, Mn, Zn, and Ni adapted to appear in the final prdouct after firing as MgO, MnO, ZnO, NiO the mol proportion of the Fezos being approximately equal to the total mol proportion of the first four oxides, adding about 0.10 to 0.20 mol proportion of the finely divided SiOz based on the mols of Fe2o3 present,

moistem'ng and plasticizin the mix, molding the mix to the desired shape and firing the molded product at a temperature to produce a two phase system consisting of a cubic crystalline phase and a glassy intercrystalline phase.

6. A process of making a shaped ferromagnetic body consisting essentially of iron oxide compounds of the magnetite type, which body consists of a heterogeneous body having a crystalline cubic phase and a glassy intercrystalline phase comprising the steps of mixing together powdered MgO, MnOz, ZnO, N10, and F8203 the mol proportion of the F6203 being approximately equal to the total mol proportion of the first four oxides, adding about 0.10 to 0.20 mol proportion of finely divided 8102 based on the mols of F6203 present, and less than 0.05 mol proportion of L (on the same basis) moistening and plasticizing the mix, with a wax emulsion, molding the mix to the desired shape and firing the molded product at a temperature to produce a two phase system consisting of a cubic crystalline phase and a glassy intercrystalline phase.

ERNST ALBERS-SCHOENBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,881,711 Lathrop Oct. 11, 1932 2,382,136 Crowley et a1 Aug. 14, 1945 2,452,531 Snoek Oct. 26, 1948 OTHER REFERENCES Snoek: New Development in Ferromagnetic Materials, (1944), Elsevier Publishing Co., Inc., New York, pp. 69-71. 

1. A FERROMAGNETIC CERAMIC MATERIAL CONSISTING MAINLY OF IRON OXIDE COMPOUNDS OF THE MAGNETITETYPE, SUITABLE FOR THE USE AT FREQUENCIES BETWEEN 60 CS. AND ABOUT 30 MCS., COMPOSED OF THE FOUR BIVALENT METAL OXIDES, MGO, MNO, ZNO, AND NIO, SILICA AND FE2O3, IN THE MOL RATIO OF.05-.35 MGO : .10-25 MNO : .15-.30 ZNO : .15-.40 NIKO : .10-20 SIO2 : ABOUT 1 FE2O3 THE TOTAL MOL PROPORTION OF THE BIVALENT METAL OXIDES TO FE2O3 BEING APPROXIMATELY 1:1 SAID MATERIAL HAVING A CURIE POINT OF AT LEAST 250* C. AN INITIAL PERMEABILITY BETWEEN 50 AND 150 AND A TEMPERATURE COEFFICIENT OF U (MEASURED ON A TOROID) OF LESS THAN 10% BETWEEN ROOM TEMPERATURE AND 120* C. 